Today, gas turbines are often constructed so that the air stream guided through them is passed through two combustors and accordingly is guided twice through turbines. The drawn-in air is hereby passed first through a compressor group, and then into a primary combustor where supplied fuel/air mixture is ignited and burned. The hot combustion air then flows from the primary combustor through a first turbine, and is fed downstream from the first turbine into a secondary combustor where fuel and, if necessary, more auxiliary air, is mixed in and ignites the mixture. Since the gases flowing out of the first turbine are frequently very hot, i.e., are above the self-ignition temperature of the fuels, an active ignition in the secondary combustor is in most cases not necessary. Downstream from the secondary combustor is a second turbine, through which the hot combustion gases from the secondary combustor flow.
For space reasons and for technical simplification, the individual components in such gas turbines are provided mostly in series along a main axis of the gas turbine. Such a gas turbo group is known, for example, from U.S. Pat. No. 5,577,378. The individual channels for the air streams and combustors all are hereby designed in most cases essentially in the form of hollow cylinders extending around the axis of the gas turbine.
Secondary combustors for such gas turbines are, as a rule, designed in a relatively simple manner since they do not need burners, but the fuel can be simply injected into the air stream via nozzles following a suitable swirling of the hot air exiting the first turbine, and the mixture self-ignites after a characteristic time. A simple, hollow-cylindrically designed secondary combustor is known, for example, from U.S. Pat. No. 5,497,611.
Because of the high mach values in secondary combustors that are necessary, for example, among other things, because of the short self-ignition times especially of gaseous fuels, thermoacoustic oscillations with high amplitudes frequently occur in the secondary combustors. In addition, there is the problem of a quick and effective mixing of air and fuel in the combustion chamber while at the same time preventing a backflow. In most cases, specific swirl-generating elements are provided for this purpose. In addition, it must be ensured during the mixing and during the combustion control, especially in more recent times, that the emission values remain within the legally permissible limits.